Direct Shear and Pull-Out Friction Testing Methods
The geosynthetic direct shear and pull-out friction testing system is designed to perform both types of tests efficiently. It allows for easy disassembly when switching between the two methods. Today, we’ll walk you through the direct shear friction test method and the pull-out friction test method in detail.
Direct Shear Friction Test Method
1. Place the sample flat on a rigid horizontal base located in the lower part of the shear box, with the front end clamped within the shear zone. If using adhesive, ensure it is applied between the sample and the base (if applicable). The alumina standard friction base can be used without bonding. After bonding, the specimen must be smooth, without folds or wrinkles. No relative slippage should occur between the sample and the base during the test.
P80
2. Install the upper shear box by filling it with standard sand of pre-determined quality, ensuring a thickness of 50mm. The sand should be evenly distributed, and the dry density after compaction should be 1750kg/m³.
3. Mount the horizontal loading device and apply an initial normal pressure of 50kPa (use a benchmark weight of 50kPa, and add three standard weights to increase the pressure by 50kPa increments).
4. Apply a horizontal load at a rate of 1mm/min ± 0.2mm/min. Measure the shear force continuously or indirectly, while recording the corresponding displacement (ΔL) at intervals of 12 seconds. The test continues until the cut surface reaches 16.5% of the total length, at which point the test will stop automatically.
5. Steps for operation:
1) Turn on the power switch.
2) Enter the password "600" to access the system.
3) Press the operation key to start a new test and enter the required speed.
Screen display: “shear forceâ€, “shear stressâ€, “peakâ€, “displacementâ€.
4) Press the start button to begin the test (incremental stress, first test at 50kPa). The result is valid, and the system automatically proceeds to the next pressure level: 100kPa, 150kPa, and 200kPa.
5) Once the displacement starts, the system completes the total contact surface. When the 16.5% cut length is reached, the machine stops, and the data is displayed. Confirm the results if they are correct.
6) Open the result query to view the test data.
7) Press OK to print the report, and the printer will automatically generate the test results.
Pull-Out Friction Test Method
1. Cut the specimen according to specifications. The width should be slightly less than the test chamber’s width, and the length should be sufficient to prevent breakage during the test.
2. Each test group should include at least 3 samples.
3. Reinforce the ends of the specimens taken from the test chamber to prevent excessive deformation during the test.
4. Fill the lower part of the test box carefully with soil based on design requirements. Ensure the fill height is flush with the seam and the soil surface is leveled.
5. Place the specimen on the soil surface, aligning the pull-out end with the seam. Ensure symmetry on both sides and gently lay a layer of soil over the specimen to position it correctly.
6. Fill the upper half of the box with soil according to the specified density and conditions.
7. Secure the end of the specimen into the tension clamp and clamp it evenly at the center.
8. Place the top cover and apply the normal pressure. Allow time for consolidation as per the test procedure.
9. Adjust the horizontal loading device and set the test parameters. Start the test. Use the up/down arrow keys to adjust the fixture position. The pull-out begins when the tension clamp starts to engage. Press the start button to record displacement and horizontal pull. The pulling rate is typically around 5mm/min for sandy soils.
10. Continue pulling until the peak pull-out force is reached and then maintain the force until it stabilizes. Stop the test at this point.
11. Replace the specimen and apply a new normal pressure. Repeat the process to complete all tests.
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